Patent Grant
10352565
This application is a National Stage of International Application No. PCT/JP2013/004768, filed Aug. 7, 2013, claiming priority based on Japanese Patent Application No. 2012-175845, filed Aug. 8, 2012, the contents of all of which are incorporated herein by reference in their entirety.
The present invention relates to a glow plug.
A glow plug is used as an auxiliary heat source for a compression ignition internal combustion engine (such as a diesel engine). In one known technique for the glow plug, a rod-shaped inner shaft and a rod-shaped ceramic heater disposed at the front end of the inner shaft are connected through a conductive ring member (for example, Japanese Patent Application Laid-Open (kokai) No. 2006-153338).
However, when the inner shaft and the ceramic heater are connected through the ring member, the heater must be press-fitted into the axial bore of the ring member. Therefore, residual stress produced as a result of press-fitting remains in the heater with the ring member attached thereto. When such residual stress remains, the heater may break easily, for example, upon reception of impact. In addition, there is a risk that when the heater is press-fitted into the axial bore of the ring member, the heater easily breaks. When the diameter of the axial bore of the ring member is made excessively large as compared with the diameter of the heater in order to facilitate press-fitting, the contact pressure between the heater and the ring member attached thereto decreases, so the contact resistance therebetween may increase.
To solve, at least partially, the above problems, the present invention can be embodied in the following modes.
(1) One mode of the present invention is a glow plug comprising a rod-shaped heater extending along an axis and including a resistance heating element held inside the heater; a tubular metallic shell which accommodates the heater with a front end portion of the heater protruding from the metallic shell; a rod-shaped inner shaft which is accommodated in the metallic shell and to which electric current is applied externally; and a conductive tubular member disposed inside the metallic shell, the tubular member having a first end with an opening into which a rear end portion of the heater is press-fitted and a second end with an opening into which a front end portion of the inner shaft is inserted, whereby the resistance heating element of the heater and the inner shaft are electrically connected to each other. The glow plug is characterized in that the heater includes an electrode terminal portion formed on an outer circumferential surface thereof and electrically connected to the resistance heating element, the tubular member includes an intermediate portion located between the first end and the second end and in contact with the electrode terminal portion, and a wall thickness of the tubular member at the first end is smaller than a wall thickness of the tubular member at the intermediate portion. In the glow plug of this mode, the contact pressure acting on the heater from the first end of the tubular member is lower than the contact pressure acting on the heater from the intermediate portion of the tubular member. Therefore, breakage of the heater when or after the heater is press-fitted into the tubular member is prevented. Since the contact pressure acting on the electrode terminal portion of the heater from the intermediate portion of the tubular member is secured, an increase in the contact resistance between the tubular member and the heater is suppressed.
(2) In the glow plug of the above-described mode, a wall thickness of the tubular member at the second end may be smaller than the wall thickness of the tubular member at the intermediate portion. In the glow plug of this mode, breakage of the heater is prevented regardless of whether the heater is press-fitted into the first or second end of the tubular member. Therefore, it is not necessary to check the orientation of the tubular member when the heater is press-fitted into the tubular member. This saves time and effort required to orient the tubular member during a production process for the glow plug, so that production cost can be reduced. In addition, the inner shaft can be easily attached to the tubular member.
(3) In the glow plug of the above-described mode, the tubular member may increase in wall thickness continuously from the first end toward the intermediate portion. In the glow plug of this mode, the contact pressure acting on the rear end portion of the heater from the tubular member increases continuously from the first end of the tubular member toward its intermediate portion. Therefore, the breakage of the heater is further prevented.
(4) In the glow plug of the above-described mode, a distance between the electrode terminal portion of the heater and an end face of the tubular member located at the first end and having the opening may be 0.6 mm or more. In the glow plug of this mode, an increase in the contact resistance between the tubular member and the electrode terminal portion is suppressed.
(5) In the glow plug of the above-described mode, the tubular member may have a thick walled portion including the intermediate portion and having a wall thickness equal to or greater than the average of the minimum and maximum values of the wall thickness of the tubular member, and the thick walled portion may be disposed so as to entirely cover at least a region extending 0.6 mm from an outer circumference of the electrode terminal portion of the heater. In the glow plug of this mode, the increase in the contact resistance between the tubular member and the electrode terminal portion is further suppressed.
(6) In the glow plug of the above-described mode, a distance between an outer circumferential surface of the tubular member and an inner circumferential surface of the metallic shell may be at least 0.2 mm. In the glow plug of this mode, the occurrence of a short circuit between the tubular member and the metallic shell is suppressed.
(7) In the glow plug of the above-described mode, the tubular member may be configured such that an area of a cross section thereof that is perpendicular to a virtual center axis of the tubular member and is taken at a minimum wall-thickness portion having a minimum wall thickness is determined on the basis of a 0.2% proof stress of a material forming the tubular member. In the glow plug of this mode, the strength of the minimum wall-thickness portion can be secured such that deformation of the tubular member when the heater is press-fitted is suppressed.
(8) In the glow plug of the above-described mode, the tubular member may be formed of a material having a 0.2% proof stress of 130 kgf/mm2 or less, and the area of the cross section at the minimum wall-thickness portion may be 1.5 mm2 or more. In the glow plug of this mode, the deformation of the tubular member when the heater is press-fitted is more reliably suppressed.
(9) In the glow plug of the above-described mode, the tubular member may be in contact with the electrode terminal portion at a position at which the tubular member has the maximum wall thickness. In the glow plug of this mode, the contact resistance between the tubular member and the electrode terminal portion is reduced.
The present invention can be implemented in various forms. For example, the present invention can be implemented in forms such as a tubular member for connecting an inner shaft and a heater, an internal combustion engine including a glow plug, and a method of producing a glow plug. The present invention is not limited to the above-described forms, and it will be appreciated that the present invention can be implemented in various forms without departing from the spirit of the invention.
The glow plug 1 includes a metallic shell 10, an inner shaft 20, the ceramic heater 30, a tubular member 40, a sleeve 50, an insulating member 60, and the annular member 70. The metallic shell 10 has a substantially tubular outer shape and accommodates the inner shaft 20. The inner shaft 20 has a substantially rod-like outer shape, and its rear end portion 26 protrudes from the metallic shell 10. A front end portion 22 of the inner shaft 20 is disposed so as to face a rear end portion 38 of the ceramic heater 30. The ceramic heater 30 has a substantially rod-like outer shape and is held by the sleeve 50 with a front end portion 36 of the ceramic heater 30 protruding from the sleeve 50. The tubular member 40 is disposed inside an axial bore 13 of the metallic shell 10 and connects the front end portion 22 of the inner shaft 20 to the rear end portion 38 of the ceramic heater 30. The sleeve 50 has a substantially tubular outer shape and is joined to the front end of the metallic shell 10. The insulating member 60 and an O-ring 65 are disposed between the rear opening of the metallic shell 10 and the inner shaft 20. The annular member 70 is disposed rearward of the insulating member 60. The glow plug 1 is configured such that the virtual center axes of the metallic shell 10, the inner shaft 20, the ceramic heater 30, the tubular member 40, and the sleeve 50 coincide with the virtual center axis of the glow plug 1.
The metallic shell 10 is formed of, for example, carbon steel or stainless steel and includes a mounting screw portion 11, a tool engagement portion 12, and the axial bore 13. The mounting screw portion 11 is a portion having a screw thread and is screwed into a screw hole of a diesel engine head (not shown). The tool engagement portion 12 is a portion for engagement with an attachment tool and is formed rearward of the mounting screw portion 11. The axial bore 13 is a hollow space extending in the axial direction of the metallic shell 10, and the inner shaft 20, the tubular member 40, and the rear end portion 38 of the ceramic heater 30 are disposed in the axial bore 13.
The inner shaft 20 is formed of an electrically conductive material such as carbon steel or stainless steel and includes, at the front end portion 22, a small-diameter portion 23 and a step portion 25. The small-diameter portion 23 is formed such that its outer diameter is smaller than the outer diameter of a main shaft portion 24 which is a portion of the inner shaft 20 and is located rearward of the small-diameter portion 23. The step portion 25 is a step formed at the boundary between the small-diameter portion 23 and the main shaft portion 24 and has an annular surface facing frontward. The inner shaft 20 is electrically connected at its front end portion 22 to the ceramic heater 30 through the conductive tubular member 40 (the details will be described later). The rear end portion 26 of the inner shaft 20 protrudes from the metallic shell 10 and forms, in cooperation with the conductive annular member 70, a terminal portion of the glow plug 1. This terminal is connected to an external power source (not shown). The power of the external power source is thereby led to the ceramic heater 30 through the inner shaft 20.
The ceramic heater 30 includes a substantially rod-shaped insulating ceramic base 31. A heating element 32 and first and second lead portions 33a and 33b are embedded in the ceramic base 31. The heating element 32 is composed of a U-shaped conductive ceramic member that is disposed in the ceramic heater 30 to be located at its front end portion 36. The first lead portion 33a connects one end of the heating element 32 to a first electrode terminal portion 34, and the second lead portion 33b connects the other end of the heating element 32 to a second electrode terminal portion 35. In the following description, the first and second lead portions 33a and 33b may be collectively referred to simply as “lead portions 33.” The first and second electrode terminal portions 34 and 35 are electrodes exposed at an outer circumferential surface 37 of the ceramic base 31. The first electrode terminal portion 34 is formed at a position closer to the rear end portion 38 than the second electrode terminal portion 35 and is in contact with the inner circumferential surface of the tubular member 40. The second electrode terminal portion 35 is in contact with the inner circumferential surface of the sleeve 50.
The tubular member 40 is a substantially tubular conductive member having an axial bore 41. The small-diameter portion 23 of the inner shaft 20 is press-fitted into the axial bore 41, and the rear end portion 38 of the ceramic heater 30 is also press-fitted into the axial bore 41, whereby the tubular member 40 holds the inner shaft 20 and the ceramic heater 30. As described above, the wall surface of the axial bore 41 of the tubular member 40 is in contact with the first electrode terminal portion 34 of the ceramic heater 30. The inner shaft 20 and the heating element 32 of the ceramic heater 30 are thereby electrically connected to each other through the tubular member 40. The tubular member 40 is spaced apart from the wall surface of the axial bore 13 of the metallic shell 10 and is thereby insulated from the metallic shell 10. The details of the shape of the tubular member 40 will be described later.
The sleeve 50 is formed of, for example, stainless steel and has an axial bore 51 and a small-diameter portion 52. The axial bore 51 is a hollow space extending in the axial direction of the sleeve 50, and the ceramic heater 30 is inserted into the axial bore 51. As described above, the wall surface of the axial bore 51 of the sleeve 50 is in contact with the second electrode terminal portion 35 of the ceramic heater 30. The heating element 32 of the ceramic heater 30 and the metallic shell 10 are thereby electrically connected to each other through the sleeve 50. The small-diameter portion 52 at the rear end of the sleeve 50 is a portion formed such that the outer diameter of the small-diameter portion 52 is smaller than the outer diameter of the rear portion of the sleeve 50. The small-diameter portion 52 is inserted into the front opening of the metallic shell 10.
The insulating member 60 is an annular member and is fitted into the rear opening of the metallic shell 10 with the inner shaft 20 inserted into the axial bore of the insulating member 60. The inner shaft 20 is thereby held by the metallic shell 10 with the electrical insulation between the metallic shell 10 and the inner shaft 20 being ensured. The O-ring 65 is attached to the outer circumference of the inner shaft 20 and disposed between the front end face of the insulating member 60 and the inner circumferential surface of the metallic shell 10. In this manner, airtightness inside the glow plug 1 is ensured. The annular member 70 is an annular conductive member and forms, together with the rear end portion 26 of the inner shaft 20, the terminal portion of the glow plug 1, as described above. The annular member 70 is disposed rearward of the insulating member 60 with the inner shaft 20 inserted into the axial bore of the annular member 70. The glow plug 1 may include, instead of the terminal portion composed of the rear end portion 26 of the inner shaft 20 and the annular member 70, a terminal portion composed of a portion of the inner shaft 20 that protrudes from the insulating member 60 and an external terminal that covers the protruding portion.
The tubular member 40 has a substantially barrel-like outer shape, i.e., a central portion (with respect to the direction of the axis CA) of the outer circumferential surface 45 of the tubular member 40 bulges outward (
The tubular member 40 is formed such that a wall thickness Te1 at the front end portion 42 is smaller than a wall thickness Tm at the intermediate portion 46 (Tm>Te1). A “wall thickness” is a thickness of the tubular member 40 in a cross section perpendicular to the virtual center axis CA and is the difference between the distance from the virtual center axis CA to the outer circumferential surface 45 in the cross section and the distance from the virtual center axis CA to the inner circumferential surface 44 in the cross section. The wall thickness Te1 at the front end portion 42 is the width of the front end face 42ef. The wall thickness Tm at the intermediate portion 46 is the average wall thickness at the intermediate portion 46.
When the wall thickness Te1 at the front end portion 42 is smaller than the wall thickness Tm at the intermediate portion 46, the tightening force of the tubular member 40 acting on the ceramic heater 30 in a region around the front end portion 42 is smaller than that in a region around the intermediate portion 46. More specifically, the contact pressure between the tubular member 40 and the ceramic heater 30 in a region around the front end portion 42 is smaller than that in a region around the intermediate portion 46. When the contact pressure in a region around the front end portion 42 is small, the occurrence of breakage of the ceramic heater 30 in a region around the front end portion 42 is suppressed. The reason for this will be described later. In the tubular member 40 of the present embodiment, the outer circumferential surface 45 has a curved shape extending in the direction of the axis CA, and the wall thickness increases continuously from the front end portion 42 toward the intermediate portion 46. Therefore, the tightening force of the tubular member 40 acting on the ceramic heater 30 increases continuously from the front end portion 42 toward the intermediate portion 46. The occurrence of breakage of the ceramic heater 30 due to attachment of the tubular member 40 thereto is thereby suppressed. The reason for this will also be described later.
In addition, in the tubular member 40 of the present embodiment, a wall thickness Te2 at the rear end portion 43 is smaller than the wall thickness Tm at the intermediate portion 46 (Tm>Te2). With this configuration, breakage of the ceramic heater 30 is prevented regardless of whether the ceramic heater 30 is press-fitted into the front end portion 42 or the rear end portion 43. Therefore, it is not necessary to check the orientation of the tubular member 40 in the direction of the axis CA when the ceramic heater 30 is press-fitted into the tubular member 40. This saves time and effort required to orient the tubular member 40 during the production process, so that production cost can be reduced. In addition, the inner shaft 20 can be easily attached to the tubular member 40.
The tubular member 40 of the present embodiment is configured such that the wall thickness gradually decreases from the intermediate portion 46 toward the front end portion 42. Therefore, the compressive stress FC produced in the ceramic heater 30 as a result of compression by the tubular member 40 gradually decreases from the intermediate portion 46 toward the front end portion 42. However, in the conventional tubular member 40c, since the wall thickness Tc is constant, the compressive stress FCc produced in the ceramic heater 30 as a result of compression by the tubular member 40c is constant at any axial position. Therefore, the compressive stress FC in a region around the front end portion 42 of the tubular member 40 of the present embodiment is smaller than the compressive stress FCc in a region around the front end portion 42c of the conventional tubular member 40c. Therefore, in the tubular member 40 of the present embodiment, the press-fitting load required when the ceramic heater 30 is press-fitted into the axial bore 41 of the tubular member 40 can be reduced. The reduction in the press-fitting load suppresses, for example, the occurrence of breakage of the ceramic heater 30 during press-fitting.
The compressive stress FC in a region around the intermediate portion 46 of the tubular member 40 of the present embodiment is substantially the same as the compressive stress FCc at a corresponding portion 46c of the conventional tubular member 40c. Therefore, in the tubular member 40 of the present embodiment, a sufficiently large contact pressure is produced at the contact surface between the tubular member 40 and the first electrode terminal portion 34 of the ceramic heater 30, and an increase in the contact resistance between the tubular member 40 and the first electrode terminal portion 34 of the ceramic heater 30 is suppressed.
In any of the tubular member 40 of the present embodiment and the conventional tubular member 40c, tensile stress FT (FTc) in a direction toward the axial bore 41, 41c is produced as residual stress in a region near the surface of a portion of the ceramic heater 30 that protrudes from the axial bore 41, 41c. The tensile stress FT (FTc) is a force produced when the ceramic heater 30 is compressed in a region near the front end portion 42, 42c of the tubular member 40 (40c) and the outer circumferential surface 37 of the ceramic heater 30 is thereby stretched. The tensile stress FT (FTc) increases in proportion to the magnitude of the compressive stress FC (FCc) in a region around the front end portions 42, 42c. As described above, in the tubular member 40 of the present embodiment, the compressive stress FC in a region around the front end portion 42 is smaller than the compressive stress FCc in the conventional tubular member 40c. Therefore, the tensile stress FT produced in the ceramic heater 30 press-fitted into the tubular member 40 of the present embodiment is smaller than the tensile FTc produced in the ceramic heater 30 press-fitted into the conventional tubular member 40c. In the tubular member 40 of the present embodiment, the occurrence of breakage of the ceramic heater 30 press-fitted into the axial bore 41 of the tubular member 40 is thereby suppressed.
As described above, in the glow plug 1 of the first embodiment, since the wall thickness Te1 at the front end portion 42 of the tubular member 40 is smaller than the wall thickness Tm at the intermediate portion 46, the occurrence of breakage of the ceramic heater 30 is suppressed. More specifically, since the tubular member 40 of the present embodiment has a reduced thickness in a region around the front end portion 42, the tightening force acting on the ceramic heater 30 is reduced in a region around the front end portion 42. Therefore, the press-fitting load required when the ceramic heater 30 is press-fitted into the axial bore 41 of the tubular member 40 is reduced, and the occurrence of breakage of the ceramic heater 30 during press-fitting is suppressed. In addition, since the compressive stress FC produced in a region around the front end portion 42 when the ceramic heater 30 is press-fitted into the tubular member 40 is reduced, the residual stress remaining in the ceramic heater 30 is reduced, and the occurrence of breakage of the ceramic heater 30 press-fitted into the tubular member 40 is thereby suppressed. Therefore, the vibration resistance and shock resistance of the glow plug 1 are improved. In addition, by reducing the wall thickness Te1 at the front end portion 42, production cost can be reduced.
In the glow plug 1 of the first embodiment, the tubular member 40 is in contact with the first electrode terminal portion 34 of the ceramic heater 30 in a region around the intermediate portion 46 having a wall thickness larger than the wall thickness of the front end portion 42. Therefore, an increase in the contact resistance between the tubular member 40 and the first electrode terminal portion 34 of the ceramic heater 30 is suppressed. More specifically, in the tubular member 40 of the present embodiment, since the wall thickness Tm at the intermediate portion 46 is larger than the wall thickness Te1 at the front end portion 42, the contact pressure applied to the ceramic heater 30 becomes sufficiently large in a region around the intermediate portion 46. Therefore, the increase in the contact resistance between the tubular member 40 and the first electrode terminal portion 34 of the ceramic heater 30 is suppressed, and a reduction in the heat generation efficiency of the glow plug 1 is suppressed.
In addition, in the glow plug 1 of the first embodiment, the wall thickness Te2 at the rear end portion 43 of the tubular member 40 is smaller than the wall thickness Tm at the intermediate portion 46. Therefore, even when the ceramic heater 30 is attached to the rear end portion 43, the stress generated in the ceramic heater 30 is suppressed, and the occurrence of breakage of the ceramic heater 30 is thereby suppressed. Since the ceramic heater 30 can be attached to any of the end portions 42 and 43 of the tubular member 40, it is not necessary to check the axial orientation of the tubular member 40 when the ceramic heater 30 is press-fitted into the tubular member 40. This saves time and effort required to orient the tubular member 40 during the production process, so that production cost can be reduced. In addition, the inner shaft 20 can be easily attached to the tubular member 40.
Moreover, in the glow plug 1 of the first embodiment, the tubular member 40 is formed such that the wall thickness increases continuously from the front end portion 42 toward the intermediate portion 46. Therefore, the contact pressure acting on the ceramic heater 30 increases continuously from the front end portion 42 toward the intermediate portion 46, and the compressive stress FC produced in the ceramic heater 30 increases continuously from the front end portion 42 toward the intermediate portion 46. Therefore, the residual stress remaining in the ceramic heater 30 due to variations in the magnitude of the compressive stress FC is thereby suppressed, so that the occurrence of breakage of the ceramic heater 30 is further suppressed.
The glow plug 1A of the second embodiment has the same configuration as that of the glow plug 1 of the first embodiment except that the placement position of the first electrode terminal portion 34 with respect to the tubular member 40 is specified. The tubular member 40 of the glow plug 1A of the second embodiment has the same configuration as that described in the first embodiment. In the glow plug 1A of the second embodiment, the first electrode terminal portion 34 is disposed in a region spaced a prescribed first distance D1 apart from the front end opening 42op of the front end portion 42 of the tubular member 40. In addition, the first electrode terminal portion 34 is disposed at a position determined such that a region extending a prescribed second distance D2 from the periphery of the first electrode terminal portion 34 (this region is represented by a chain double-dashed line in
The present inventor has found that the above-described prescribed first and second distances D1 and D2 for specifying the placement position of the first electrode terminal portion 34 with respect to the tubular member 40 are each preferably 0.6 mm or more (D1, D2≥0.6 mm). As described later, when the two distances D1 and D2 are each 0.6 mm or more, deterioration of the first electrode terminal portion 34 is suppressed, and a reduction in heat generation efficiency of the ceramic heater 30 is suppressed. The tubular member 40 may be thermally expanded when placed in, for example, a high-temperature environment of 100° C. or higher. When at least the first distance D1 is 0.6 mm or more, oxygen entering the gap between the tubular member 40 and the ceramic heater 30 through the front end opening 42op of the tubular member 40 is restrained from reaching the first electrode terminal portion 34 even when the tubular member 40 is thermally expanded. When the second distance D2, as well as the first distance D1, is 0.6 mm or more, a distance that can restrain oxygen from reaching the first electrode terminal portion 34 is ensured over the entire periphery of the first electrode terminal portion 34, and the contact pressure acting on this peripheral region from the tubular member 40 is ensured by the thick walled portion 47. Therefore, oxygen is more reliably restrained from reaching the first electrode terminal portion 34. When oxygen is restrained from reaching the first electrode terminal portion 34, oxidation of the first electrode terminal portion 34 is suppressed, and an increase in contact resistance between the tubular member 40 and the first electrode terminal portion 34 is suppressed. Therefore, a reduction in the heat generation efficiency of the ceramic heater 30 is suppressed.
As described above, in the glow plug 1A of the second embodiment, the first electrode terminal portion 34 of the ceramic heater 30 is disposed at a suitable position with respect to the tubular member 40, so that oxidation of the first electrode terminal portion 34 is suppressed. Therefore, a reduction in the heat generation efficiency of the ceramic heater 30 is suppressed.
As described above, in the glow plug 1B of the third embodiment, the separation distance C between the metallic shell 10 and the tubular member 40 is properly determined, so that the occurrence of a short circuit between the metallic shell 10 and the tubular member 40 is suppressed. Therefore, a reduction in the heat generation efficiency of the ceramic heater 30 is suppressed.
In the tubular member 40 of the fourth embodiment, the area Smin of a cross section perpendicular to the direction of the axis CA and taken at a portion at which the wall thickness Tm is minimum (this portion may be hereinafter referred to as a “minimum wall-thickness portion”) is specified as follows. The area Smin of the cross section of the minimum wall-thickness portion is specified such that a load in the direction of the axis CA applied to the tubular member 40 when the ceramic heater 30 is press-fitted thereinto (this load is hereinafter referred to as a “press-fitting load”) does not produce a stress larger than 0.2% proof stress in the minimum wall-thickness portion. More specifically, the area Smin of the cross section of the minimum wall-thickness portion is specified as a value equal to or larger than a value obtained by dividing an estimated maximum value Lmax of the press-fitting load by an upper limit stress Pmax that is the upper limit of stress at which permanent strain in the material forming the tubular member 40 is suppressed to 0.2% (formula (1) below). The upper limit stress Pmax corresponds to the 0.2% proof stress of the material forming the tubular member 40.
Smin≥Lmax/Pmax (1)
In the tubular member 40 of the present embodiment, the wall thicknesses Te1 and Te2 at the front end face 42ef and the rear end face 43ef are each the minimum thickness Tmin, and therefore the front end face 42ef and the rear end face 43ef each correspond to the cross section of the minimum wall-thickness portion. Since the area Smin of the cross section of the minimum wall-thickness portion is specified on the basis of the 0.2% proof stress of the material forming the tubular member 40 as described above, the strength of the tubular member 40 against press-fitting of the ceramic heater 30 thereinto is ensured even at the minimum wall-thickness portion having the lowest strength. Therefore, deformation of the tubular member 40 when the ceramic heater 30 is press-fitted is suppressed.
Smin≥200 [kgf]/130 [kgf/mm2]=1.5 [mm2]
More specifically, when the tubular member 40 is formed of a material with a 0.2% proof stress of 130 kgf/mm2 or less, the area Smin of the cross section of the minimum wall-thickness portion is specified to be 1.5 mm2 or more, and deformation of the tubular member 40 when the ceramic heater 30 is press-fitted thereinto is thereby suppressed. In this case, it is more preferable that the area Smin of the cross section of the minimum wall-thickness portion is 2 mm2 or more. When the area Smin of the cross section of the minimum wall-thickness portion is 1.5 mm2 and the outer diameter ϕCH of the ceramic heater 30 is 3.1 mm, it is preferable that the minimum thickness Tmin of the tubular member 40 is specified as follows.
Tmin=(ϕmin−ϕCH)/2=0.15
ϕmin: the outer diameter of the minimum wall-thickness portion
ϕmin=[{(Smin+SCH)}/π]^(½)]×2
As described above, in the glow plug of the fourth embodiment, since the lower limit of the cross-sectional area of the minimum wall-thickness portion of the tubular member 40 is specified on the basis of the 0.2% proof stress of the constituent material, deformation and damage caused by press-fitting of the ceramic heater 40 are suppressed.
The present invention is not limited to the above-described embodiments and may be embodied in various forms without departing from the scope of the invention. For example, the following modifications are possible.
In the first embodiment described above, the wall thickness Te1 at the front end portion 42 of the tubular member 40, the wall thickness Tm at the intermediate portion 46, and the wall thickness Tc of the conventional tubular member 40c satisfy the relation Te1<Tc≅Tm. However, the wall thicknesses Te1 and Tm of the tubular member 40 in each of the above embodiments and the wall thickness Tc of the conventional tubular member 40c may satisfy the relation Te1<Tm<Tc or may satisfy the relation Te1<Tc<Tm.
In the first embodiment described above, the wall thickness Tm at the intermediate portion 46 of the tubular member 40 is the average wall thickness of the intermediate portion 46. However, the wall thickness Tm at the intermediate portion 46 may be the maximum wall thickness of the intermediate portion 46 or the minimum wall thickness thereof.
In the first embodiment described above, the ceramic heater 30 is press-fitted into the tubular member 40 from the rear end opening 43op during assembly of the glow plug 1. However, in the tubular member 40 in any of the embodiments, the ceramic heater 30 may be press-fitted from the front end opening 42op.
In the glow plugs in the above embodiments, the diameter of the axial bore 41 of the tubular member 40 is substantially constant in the direction of the axis CA. However, the axial bore 41 of the tubular member 40 may vary in the direction of the axis CA.
In each of the above embodiments, the tubular member 40 may be disposed at a position at which the first electrode terminal portion 34 is in contact with a portion of the tubular member 40 at which the wall thickness is maximum. In this configuration, the contact pressure acting on the first electrode terminal portion 34 from the tubular member 40 is more reliably secured, so that the heat generation efficiency of the ceramic heater 30 is ensured.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-175845 | Aug 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/004768 | 8/7/2013 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2014/024485 | 2/13/2014 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| RE31908 | Petrik | Jun 1985 | E |
| 6064039 | Kumada | May 2000 | A |
| 6881930 | Yoshikawa | Apr 2005 | B2 |
| 7223942 | Konishi | May 2007 | B2 |
| 7420139 | Yoshikawa | Sep 2008 | B2 |
| 7692118 | Itoh | Apr 2010 | B2 |
| 20050104496 | Ando | May 2005 | A1 |
| 20090184101 | Hoffman | Jul 2009 | A1 |
| 20110114622 | Sekiguchi | May 2011 | A1 |
| 20120187101 | Hatano | Jul 2012 | A1 |
| 20140196680 | Torazawa | Jul 2014 | A1 |
| Number | Date | Country |
|---|---|---|
| 09-42671 | Feb 1997 | JP |
| 2005-147533 | Jun 2005 | JP |
| 2006-153338 | Jun 2006 | JP |
| 2010-139152 | Jun 2010 | JP |
| 2010139152 | Jun 2010 | JP |
| 2010-181068 | Aug 2010 | JP |
| 2011-017478 | Jan 2011 | JP |
| Entry |
|---|
| Translation JP2010139152. |
| International Search Report of PCT/JP2013/004768 dated Sep. 3, 2013 [PCT/ISA/210]. |
| Communication dated Mar. 16, 2016, issued by the Korean Intellectual Property Office in corresponding Korean Application No. 10-2015-7005677. |
| Number | Date | Country | |
|---|---|---|---|
| 20150292739 A1 | Oct 2015 | US |
